Multiple semiconductor devices are fabricated in a matrix on a semiconductor wafer, which is typically made of material such as sapphire, silicon, gallium and/or their compounds. The semiconductor wafer is then cut by a laser to divide, or assist in dividing, the semiconductor devices into separate pieces.
Conventional laser singulation may include any of the following processes: i) laser scribing, in which linear grooves (or scribe lines) are formed on the semiconductor wafer surface to facilitate breakage along the grooves; or ii) laser cutting, in which the semiconductor wafer is cut through from its top surface to its bottom surface.
Specifically, laser singulation is contingent on delivering irradiance (i.e. fluence or energy) to the semiconductor wafer that exceeds its material ablation threshold. By focusing a laser beam using an objective lens, a laser output width of the Gaussian laser beam can be made small in the order of 1 to 20 μm. Such dimensions of the laser beam ensure that its irradiance exceeds the material ablation threshold of the semiconductor wafer for laser singulation.
FIG. 1 shows a conventional laser scribing process 100, in which a laser beam 102 is focused at a point on a surface of a semiconductor wafer 104 having semiconductor devices (not shown), before a relative motion between the laser beam 102 and the semiconductor wafer 104 is effected along a scribing direction 110 to form a scribe line 106 on the surface of the semiconductor wafer 104. However, when the laser beam 102 is focused on the surface of the semiconductor wafer 104 with the delivered irradiance at or above its material ablation threshold, debris 108 will be removed from the semiconductor wafer 104 and may redeposit back onto the surface of the semiconductor wafer 104. This may contaminate the semiconductor devices on the semiconductor wafer 104. Thus, the conventional laser singulation process has the problem of surface contamination of the semiconductor wafer 104.
One way to avoid the debris 108 from contaminating the semiconductor devices on the semiconductor wafer 104 is by performing surface coating and washing before and after laser processing. Unfortunately, the surface coating process has its own limitations. For instance, the surface and side-wall recast molten layer may affect the appearance and/or the performance of the semiconductor device after singulation. Other post-processing approaches, such as side-wall etching, have been proposed to mitigate this problem. However, extra pre- and post-processing of the surface-scribed wafer would ultimately limit the overall production yield and increase the running cost.
Thus, it is an object of this invention to at least seek to ameliorate the problems among conventional laser singulation processes.